Excretion Notes from Old Notes Flashcards
Excretion
Getting rid of stuff in your tissues
Examples:
Exhalation of CO2 is excretion
Loss of material in sweat
Urine contents from kidney
Nephrons are composed of
Bowmen’s capsule
Convoluted tubule
Loop of Henle
What enters the bowmen’s capsule?
The blood plasma minus the big proteins: this substance is called filtrate
Direction of blood flow in Kidney’s
Afferent arterioles -> glomerulus (capillary ball) -> efferent arterioles -> peritubular capillaries -> venuoles
Vasa recta
A group of peritubular capillaries that surround the loop of Henle
The outer region of the kidney
Renal Cortex
The inner region of the kidney
Renal Medulla
The bowmen’s capsule, glomerulus, convoluted tubules all are part of which region?
Cortex
The Loop of Henle is in which region of the kidney?
Extends out of the cortex and into the medulla
The entry point through the capsule
Hilum
The Glomerular Filtration Rate (GFR)
115-125 ml filtrate/min is formed in bowman’s capsule by all nephrons (total)
The bulk of filtrate will be reabsorbed
How can we regulate the filtration rate?
- We adjust it by adjusting the blood pressure in the capillaries of the glomerulus:
a. more pressure in capillary = more fluid forced out
b. less pressure in capillary = less fluid forced out
How do we adjust blood pressure in the capillaries of the glomerulus?
Dilation of arteriole; blood pressure in capillary is higher and more fluid is lost
Constriction of arteriole; blood pressure in capillary is lower and less fluid is lost
After filtrate leaves the bowman’s capsule, it goes to…
The Proximal Tubule
How much filtrate formed in the glomerulus gets reabsorbed in the proximal tubule?
Approximately 65% of the filtrate that’s formed in the glomerulus is reabsorbed in the proximal tubules
T/F: Sodium is the major solute in blood. It is actively transported into blood and chloride follows by charge attraction
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T/F: Other solutes include glucose and amino acids which are transported into capillaries via special transporters
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When the filtrate leaves the proximal convoluted tubule does it contain glucose or amino acids?
When the filtrate leaves the proximal convoluted tubules it has no glucose nor amino acids in it because it has nearly been all reabsorbed. The reasons diabetics have glucose in their urine is because their blood glucose are so high that the filtrate also has high glucose concentration. Limited number of transporter protein that can move glucose in filtrate back into blood.
What comes after the proximal tubule?
Loop of Henle
What is the function of the loop of henle?
To create a concentration gradient within the medulla tissue
It’s function is not to alter the content of the filtrate very much, its real job is just to create a concentration gradient in the medullary tissue through which the loop of henle transverse
Is the filtrate more concentrated when it enters or exits the loop of henle?
The filtrate is less concentrated when it leaves the loop of henle than when it enters it
What comes after the loop of henle?
Collecting Duct
What does ADH stand for?
Antidiuretic Hormone
Explain antidiuretic hormone
Comes from the posterior pituitary (a neurosecretion)
Also known as a vasopressin because it constricts blood vessels
Increases the water permeability in the collecting duct
What does antidiuretic mean?
Prevents loss of water
Explain what happens when ADH acts on collecting duct
The filtrate comes in collecting duct and is not very concentrated, but as it moves down the collecting tube it encounters more concentrated filtrate. Water will leave the collecting duct, concentrating the urine. The urine will be low in volume and highly concentrated
What happens when we are hydrated?
If we have too much water in our system, then we do not collect ADH and hence the walls of our collecting duct will not be permeable to water and therefore low concentrated filtrate comes in and large volume of low concentrated urine comes out
What part of our brain senses water concentration?
The Hypothalamus
Do our neurons fire or stop firing when there is too much water?
If there is too much water then neurons stop firing and there is no ADH secretion
If one is dehydrated, neurons will increase firing rate and more ADH is secreted and collecting ducts become even more permeable to water and more water is retained
Name 2 other chemicals that cause dehydration
Caffeine and alcohol both act on the hypothalamus and inhibit ADH secretion. Therefore it causes us to produce more dilute urine than you should. Dehydrating effect.
How does the loop of Henle create a concentration gradient?
The thick ascending limb is impermeable to water and solutes. Even though it is impermeable there is active transport of sodium out of filtrate. The pumping of salt out of filtrate which adds salt to the extracellular fluid in the medulla causes the increase osmotic concentration outside. It is also responsible for the low concentration of the filtrate leaving the loop of henle. The thin ascending limb of loop of henle is permeable to solutes and water.
Aldosterone
Comes from the adrenal cortex
With aldosterone up to 100% Na+ reabsorbed
K+ is secreted into filtrate
Activates Na+/K+ pump further (Na+ leaves filtrate & K+ enters)
Used to control the secretion of two ions:
Retain Na+
Excrete K+
How do we control for aldosterone secretion?
Secretion occurs when body is: low in Na+ or too much K+;
low K+ would inhibit secretion
Juxtaglomerular apparatus
It is half distal tubule and half afferent arteriole
Within the afferent arterioles are granular cells
Within the distal tubule are macula densa cells
Renin
An enzyme secreted by the granular cells
Granular cells secrete
Renin into the blood that is flowing through the afferent arteriole. Does this when the blood flow in the arteriole is lowered. The cells act like stretch receptors. High flow (high volume) the arterioles are stretch so there is no secretion. Low flow (low volume) the arterioles are not stretched as much so there is secretion of renin.
Angiotensinogen
A plasma protein produced by the liver that is always present in the blood
T/F: Renin makes angiotensinogen into angiotensin I
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Angiotensin II
The active hormone whose target organ is the adrenal cortex which triggers the secretion of aldosterone
Is also a very strong vasoconstrictor which will constrict the arterioles and increase total peripheral resistance which will also increase blood pressure as a result. In particular within the afferent arterioles leading to the glomerulus that causes the glomerulus filtration rate to fall so less fluid is lost
What is the active hormone that acts on the adrenal cortex in order to trigger the secretion of aldosterone?
Angiotensin II
What happens with renin when your blood volume is too low (such as during severe dehydration)?
There is a low flow and little stretching so,
Renin will be secreted, which will act on angiotensinogen to make angiotensin I which will go to the lungs and be converted into angiotensin II which will now act on the adrenal cortex to make aldosterone. Angiotensin II will reduce the Glomerulus filtration rate so we preserve fluid. Aldosterone increases pumping out of salt in the distal tubule which means more water will flow out of kidneys with the salt and into the blood, hence less water is lost in urine
Macula densa cells
Act to inhibit renin secretion
They are part of the distal tubule so they respond to high sodium concentration in the filtrate in the distal tubules.
What is there is too high of a sodium concentration in the blood either via high salt intake or loss of water?
You will have too high of an osmotic concentration. The hypothalamus is very sensitive to the osmotic concentration of the blood. Posterior pituitary produces antidiuretic hormone which doesn’t allow water to leave and reclaim it from the collecting dust so less water is loss in urine. Attempt to restore osmotic concentration in blood. If excess sodium was the “trigger” for the restoration of osmotic concentration in blood then adding the reabsorbed H2O creates a too large blood volume. This will cause too much stretching in the arterioles so renin production will be inhibited therefore aldosterone production will stop which will reduce salt pumping in the distal tubules and enhance fluid loss in urine. This will also stop angiotensin II production hence less vasoconstriction so the glomerulus filtration rate increases and excess fluid ends up in nephron.
Atrial Natriuetic Factor
Hormone produced when the atria is stretched too much (such as in the case of increased blood volume)
ANH wil act to eliminate fluid via:
1. Inhibit ADH from posterior pituitary
2. Inhibits renin secretion (to prevent angiotensin system where water flow into blood via osmosis)
3. Inhibits aldosterone secretion
4. Increases permeability of glomerular capillaries which therefore glomerular filtration rate increases
5. Relaxes smooth muscles in the arterioles especially the afferent arterioles which therefore increases glomerular filtration rate
How do Kidney cells in the nephron control the pH of the body fluid?
Secrete hydrogen ions into the urine
Ways to estimate glomerulus filtration rate
Use inulin which is not normally found in the body
The amount of inulin in the urine is a reflection of the amount filtered at glomerulus; related to GFR
If you inject someone with inulin you can figure out its concentration in the blood and then collect the urine and see how much of it comes out in the urine per minute thus giving you GFR
Paraaminohippuric acid
PAH
All molecules of PAH in the blood are eliminated in one pass through the kidney
It is filtered in the glomerulus
PAH that did not get filtered is then secreted into filtrate from paratubular capillaries
The clearance rate of PAH is equal to the blood flow to the kidneys
